Known apparatus for monitoring the respiratory condition, the pulse rate and so on of a living body, or subject, include those comprising one or more than one sensors to be put on the body of the subject or those adapted to observe the subject while the subject is lying still in bed. Japanese Patent Application Laid-Open No. 2002-576 discloses an apparatus comprising one or more than one contact type electrodes to be put on some of the finger tips and/or either or both of the ear lobes and/or irradiating a beam of light onto the body of the subject in order to detect necessary information. The disclosed apparatus has advantages including that it is resistant against external noises and that the components of the apparatus to be put on the subject are lightweight and compact.
On the other hand, Japanese Patent Application Laid-Open No. H10-229973 discloses an apparatus comprising one or more than one vibration detection means to be arranged in a bed or a chair in order to detect fine vibrations of the body of the subject caused by the circulation of blood of the subject who is lying on the bed or sitting on the chair, whichever appropriate, for the purpose of monitoring the biological information of the subject. FIG. 9 of the accompanying drawings schematically illustrates the disclosed apparatus. A supersonic sensor or an infrared sensor 111, which is a non-contact type sensor, can be used as vibration detection means for detecting the displacement M of the subject 112 shown in FIG. 9. A piezoelectric sensor may be used to monitor the vibrations of the body when the subject is lying on the bed. The detected vibrations of the body may be displayed on a display 113 that is buried in the head wall 110 as shown in FIG. 9.
While monitoring apparatus of the type having components to be put on the body of the subject can be handled with ease and light weight, they are neither convenient nor comfortable when used in daily lives. On the other hand, monitoring apparatus comprising components arranged in a bed or a chair are also rather inconvenient because the subject is forced to quietly keep a predetermined posture in the bed or on the chair for the purpose of monitoring. When ultrasonic waves or infrared rays are used for non-contact sensors, the subject can voluntarily take a posture that is comfortable to him or her because biological information can be acquired remotely. However, the wear and the hair of the subject reflect and absorb ultrasonic waves and infrared rays to operate as obstacles so that only limited sites can be observed by such means if the subject is clothed. Additionally, movements of the wear and those of the hair that are caused by flows and vibrations of air can enter the monitoring system as noises.